Many commercial products include portions that are made of more than one type of material, such as metal portions and plastic portions, which are assembled together into a single part. Often, an anodizing process is used to provide a protective and cosmetically appealing surface finish to the metal portions of these composite parts. During an anodizing process, a metal part is exposed to an electrolytic process whereby the metal part acts as an anode. The process forms a metal oxide film or anodic film on surfaces of metal. The metal oxide layer can enhance the durability and corrosion resistance of the part. In addition, the metal oxide layer has a porous structure that can accept any of a number of dyes. These dyes can be infused within the porous structures of the metal oxide to give the part a particular color.
Although anodizing can provide numerous benefits, the anodizing process itself can complicate the manufacturing process when a part is a composite part that includes portions made of materials that are not anodizable, such as plastic, glass or ceramic. This can be especially problematic when the anodizable metal portions are directly adjacent the non-anodizable portions. This arrangement creates gaps, even if small, between the anodizable metal portions and non-anodizable portions where chemicals from an anodizing process can get trapped. The trapped chemicals can leak out or otherwise disrupt subsequent operations. For example, the trapped chemicals can inhibit the uptake of dyes within portions of the anodic films and create visible defects, which detract from the cosmetic appearance of the composite parts.